The Risks of Getting This Wrong

Before getting into specific myths, it's worth establishing why this matters beyond the obvious: treating a normal thyroid doesn't just fail to help — it can cause real harm. The consequences of running thyroid hormone levels too high are well documented, and they fall hardest on the heart and skeleton. These aren't rare or theoretical risks. They show up in large population studies at TSH levels that some wellness providers are actively targeting.

3×
increased risk of atrial fibrillation over 10 years when TSH is below 0.1 in patients 65 and older [1]
39%
increased risk of cardiovascular death when TSH is below 0.1, in a study of over 700,000 patients [2]
3–4×
increased risk of hip and spinal fractures when TSH is consistently at or below 0.1 [1]
📊 The Evidence — Overtreatment Harms

These numbers come from studying patients with suppressed TSH — the same range that gets targeted when providers push for "optimal" low TSH levels. A large retrospective study of 705,307 US veterans found a 39% increased risk of cardiovascular death in patients with TSH below 0.1 mIU/L.[2] Subclinical hyperthyroidism — even the milder form, with TSH between 0.1 and 0.4 — is associated with a 36% increased risk of hip fracture, 28% increased risk of any fracture, and meaningful cardiac structural changes including left ventricular hypertrophy and diastolic dysfunction.[1][3]

The risk runs in both directions. Severe untreated hypothyroidism — TSH above 20 mIU/L — carries a 2.67-fold increased risk of cardiovascular death and can progress to myxedema coma, a life-threatening emergency with a mortality rate of 6.8–30%.[2] Between those extremes is the therapeutic window that evidence-based dosing is designed to stay inside.

My Synthesis When I see a patient who has been prescribed thyroid medication to achieve a TSH well below the normal range — particularly an older patient — this is not a minor concern. A TSH of 0.05 in a 70-year-old is not optimization. It's iatrogenic hyperthyroidism, and the atrial fibrillation and fracture data are why I take it seriously. The therapeutic goal is a TSH within the normal range, adjusted for the individual. Anything below 0.5 warrants a careful look at whether the dose is too high.

The Myths, One by One

Myth 1
"Your TSH should be between 1 and 2 for optimal health."
The reference range for TSH runs from roughly 0.5 to 4.0 mIU/L, and there is no good evidence that a TSH of 1.0 produces better outcomes than a TSH of 3.0 for most people on treatment. Guidelines vary on whether to aim for the lower portion of the range in younger patients, but none recommend a specific target within the normal range for the general population.[4][5] In older adults the evidence actually points the other way: a slightly higher TSH — toward the upper end of normal — appears protective and is associated with reduced mortality. Targeting a low-normal TSH in a 70-year-old increases the risk of overtreatment, atrial fibrillation, and fracture.[4]

One legitimate nuance: 15–38% of patients on levothyroxine have TSH below the reference range, indicating overtreatment — not optimization.[5] If your provider is actively pushing your TSH toward the bottom of the range or below it, that's worth questioning.
Myth 2
"Reverse T3 is blocking your thyroid receptors and making you feel terrible."
Reverse T3 (rT3) is a real molecule — it's an inactive form of T3 that the body produces as a way of regulating how much active thyroid hormone is available during times of stress or illness. Measuring it is not part of any mainstream endocrinology guideline, because there is no validated evidence that elevated reverse T3 in an otherwise normal thyroid panel causes symptoms or that treating it improves outcomes.[9]

Reverse T3 rises predictably during illness, caloric restriction, and stress — all situations where the body is intentionally reducing metabolic rate. This is a regulated response, not a malfunction. Prescribing T3 medication to "clear" reverse T3 is not supported by any clinical trial evidence, and high-dose T3 carries the cardiovascular and bone risks described above. Reverse T3 testing is offered by many direct-to-consumer labs and functional medicine providers, but a high result in an otherwise normal panel is far more likely to reflect normal physiology — or one of the conditions listed above — than a treatable thyroid problem.
Myth 3
"You have adrenal fatigue — your adrenals are burned out and affecting your thyroid."
"Adrenal fatigue" is not a recognized medical diagnosis. The American Association of Clinical Endocrinologists and the American College of Endocrinology explicitly state that the condition does not exist as a clinical entity, and that the tests marketed to diagnose it — primarily salivary cortisol panels — have not been validated against any reference standard.[6]

True adrenal insufficiency (Addison's disease and related conditions) is a real and well-defined condition caused by actual destruction or dysfunction of the adrenal glands. It is rare — affecting somewhere between 4 and 279 people per million depending on the type — and it presents with a specific constellation of findings including profound fatigue, weight loss, nausea, low blood pressure, and in primary disease, darkening of the skin.[7] It is diagnosed with morning cortisol, ACTH stimulation testing, and DHEAS measurement — not a salivary cortisol kit ordered online.

The real harm of the adrenal fatigue diagnosis is twofold. First, "adrenal support" supplements marketed as hormone-free sometimes actually contain thyroid and steroid hormones — undisclosed.[6] Second, prescribing hydrocortisone for non-existent adrenal fatigue risks suppressing the body's own adrenal function over time and can mask genuinely serious conditions that need their own evaluation.
Myth 4
"Your TSH is 'normal' but your Free T3 is low — that's why you feel bad."
A normal TSH with a low-normal free T3 is a pattern sometimes used to justify T3 supplementation in wellness settings. The problem is that free T3 assays are less reliable than TSH or free T4 — subject to more variability and interference — and there are no validated outcome data showing that treating a low-normal free T3 in the context of a normal TSH and normal free T4 improves how patients feel.[4]

People on levothyroxine monotherapy do tend to have T3 levels toward the lower end of the reference range compared to people with normal thyroid function — this is a legitimate physiologic observation and the basis for the ongoing combination therapy debate covered in Post 1.2. But "lower end of normal" is not the same as deficient, and using it as a standalone indication for T3 prescribing — without a normal TSH confirmation and a careful look at other explanations for symptoms — goes beyond what the evidence supports.
Myth 5
"Iodine supplements will support your thyroid and improve your energy."
Iodine is essential for thyroid hormone production — the thyroid uses it as a raw material, and iodine deficiency is the leading cause of hypothyroidism worldwide. In countries with iodized salt and varied diets, true iodine deficiency is rare. Supplementing beyond what the body needs does not produce more thyroid hormone or improve energy in people who are already iodine-sufficient.

In fact, excess iodine can trigger or worsen both hypothyroidism and hyperthyroidism — a phenomenon called the Jod-Basedow effect for hyperthyroidism and the Wolff-Chaikoff effect for hypothyroidism. People with underlying autoimmune thyroid disease (Hashimoto's or Graves') are particularly susceptible. High-dose iodine supplements marketed for "thyroid support" have caused new-onset thyroid disease in people whose thyroids were previously normal.[4]

A Note on "Functional" Thyroid Testing

Many of the myths above are supported by expanded thyroid panels — tests that go beyond TSH, free T4, and free T3 to include reverse T3, thyroid antibodies without clinical indication, and other markers. These panels are marketed as giving a more complete picture of thyroid health. In practice, more tests in a patient who feels unwell but has a normal TSH and free T4 generate more numbers to explain symptoms with — not more diagnostic clarity.

The standard panel that evidence-based medicine supports is TSH as the primary screen, with free T4 added when TSH is abnormal. Free T3 and thyroid antibodies have specific indications. Reverse T3 has none that are validated. Ordering a panel that returns ten thyroid-related numbers in a symptomatic patient with a normal TSH does not improve the chance of finding the real problem — it improves the chance of finding something to treat that isn't actually causing the problem.

My Synthesis I'm direct with patients who come in having been told they have reverse T3 dominance, adrenal fatigue, or an "optimal TSH" problem. I don't dismiss how they feel — the fatigue and brain fog are real, and I want to find the actual cause. What I tell them is that the wellness industry has built a framework that produces a diagnosis for almost everyone who walks through the door, because symptoms that vague are present in the general population at very high rates. A diagnosis that fits everyone doesn't tell us anything useful. The path to actually feeling better almost always runs through sleep, mental health, metabolic evaluation, and primary care — not through a thyroid panel with ten numbers and a prescription for T3.